• Posted July 31, 2026

Family History Plays Role In Genetic Risk For Breast Cancer, Researchers Find

A woman’s genetic risk for breast cancer depends on her family history as well as the presence of cancer-causing mutations, a new study says.

Breast cancer risk among women tested for BRCA gene mutations shifted depending on the cancer history of family members, researchers reported July 30 in JAMA Network Open.

Among women who tested positive for a BRCA mutation, breast cancer risk varied from roughly 56% to 86%, depending on the number of immediate family members who had breast or ovarian cancer, researchers found.

“Based on these findings, a physician might recommend more frequent mammograms or breast MRI to a BRCA-positive patient in their 50s or 60s with no family history of breast cancer, but suggest preventive mastectomy as an option for a young BRCA patient with several cases of breast cancer in the family,” lead researcher Dr. Fahima Dossa said in a news release. She is a surgical oncologist at Cedars-Sinai Medical Center in Los Angeles.

An average woman has about a 13% chance of developing breast cancer during her lifetime, researchers said in background notes.

Women with BRCA1 or BRCA2 mutations have an increased breast cancer risk of 30% to 70%, researchers said. These variants interfere with the body’s ability to repair DNA damage that can lead to cancer.

BRCA testing is recommended for women with a personal or family history of certain cancers, a known BRCA mutation in the family, or Ashkenazi Jewish ancestry, researchers said.

“While most women who undergo genetic testing do not test positive for a cancer-risk-increasing BRCA mutation, they have generally been referred for testing because of strong personal or family cancer history,” Dossa said.

“Future cancer risk for these women has not been well studied, and our findings are the first to calculate that risk so that we can better guide all women who undergo BRCA testing,” she said.

For the study, researchers analyzed the health records of nearly 16,000 women who underwent BRCA testing in Ontario, Canada between 2007 and 2016.

Results also showed that those women who tested negative for BRCA cancer-causing mutations still had a 25% lifetime risk of developing breast cancer, likely due to family history or ancestry, researchers said.

Likewise, women with BRCA mutations not known to be linked to breast cancer still had a 30% higher risk of breast cancer.

The only women in the study with the same breast cancer risk as the general population were those who had a family history of cancer and a known BRCA mutation in the family, but who did not carry that specific mutation, Dossa said.

“This study is a reminder to patients about the importance of having discussions with their doctors about genetic test results,” she said. “We finally have some data to help inform those conversations.”

More information

The National Cancer Institute has more on BRCA mutations and breast cancer.

SOURCE: Cedars-Sinai Medical Center, news release, July 30, 2026